MTEC PAC300 Manuel utilisateur

MTEC PAC300

Photoacoustic Detector

Operating Instructions

August, 2023

MTEC Photoacoustics, Inc.

3507 Oakland St.

Ames, IA 50014 USA

Telephone: 1 515 451 9234

www.mtecpas.com

[email protected]

Table of Contents

1. First and Foremost: Three Key Precautions to Protect PAC300 from Damage

1.1 Protecting Microphone during Purging ………………………………............3

1.2 Caution to Avoid Breaking Window ……………………………………………….3

1.3 Protecting Window from Moisture Damage …………………………………..3

2. Unpacking

2.1 Unsealing the Hermetically Sealed Shipping/Storage Case ……………..3

2.2 Packing List …………………………………………………………………………………...3

2.3 Damage Inspection …………………………………………………………………………4

3. PAC300 Description

3.1 Introduction to the PAC300 ………………………………………………………………….4

4. Set-Up Directions

4.1 Insert Rear Lever …………………………………………………………………………….5

4.2 Mounting and Alignment of the PAC300 in the FTIR ……………………..…6

4.3 Electrical Connections …………………………………………………………………….9

4.4 Purge Gas Connections …………………………………………………………………..10

5. Operation

5.1 Preamplifier Gain Control …………………………………………………………..….10

5.2 Rear Lever Operation …………………………………………………………………….11

5.3 Sample Cup Loading ……………………………………………………………………..11

5.4 Sample Cup Insertion …………………………………………………………………..…13

5.5 Purging ………………………………………………………………………………………....14

5.6 FTIR Spectrum Acquisition Parameters ………………………………………..…14

5.7 Test Procedure ……………………………………………………………………………….15

5.8 Acquiring and Normalizing a Sample Spectrum …………………………..…15

5.9 Advanced Methods of Photoacoustic Spectroscopy ……………………...16

5.10 Storage of the PAC30 ……………………………………………………………………16

6. User Adjustments and Servicing

6.1 Setting the Sample and Reference Cup O-ring Seal Compression …..17

6.2 Window Replacement ……………………………………………………………………17

7. Service Assistance

7.1 Returning Units for Factory Servicing ……………………………………………..19

7.2 Foreign Returns ……………………………………………………………………………….19

8. Product Warranty and Disclaimer …………………………………………………………………..….20

1. First and Foremost: Three Key Precautions to Protect PAC300 from Damage

1.1 Protecting Microphone during Purging

Purging with zero grade helium gas is used to enhance the sensitivity of photoacoustic

measurements and to reduce the moisture level in the sample chamber which

superimposes a water vapor spectrum on the sample spectrum and also interferes with

condensed sample signal generation. However, a too high gas flow rate can easily damage

the PAC300’s sensitive microphone. Accidental high flow rates may occur when gas valves

are being opened or adjusted. The PAC300 microphone is protected from gas flow surges

as long as the rear lever is in the SEAL position.

1.2 Caution to Avoid Breaking Window

Do not place samples in the brass sample cup that extend above 1 mm from the top of the

cup. Samples that extend above the top of the cup will break the PAC300’s window.

1.3 Protecting Window from Moisture Damage

The PAC300’s KBr window is moisture sensitive. The window can be protected from

moisture damage by storing the unit in its hermetically sealed case with a 10 g packet of

indicating silica gel ( http://silicagelpackets.com/indicating-silica-gel-packets/indicating-

silica-gel-packets/10-gram-indicating.html ).

2. Unpacking

2.1 Unsealing the Hermetically Sealed Shipping/Storage Case

In cold weather, it is advisable to let the case warm up for 24 hrs. before opening to

prevent moisture condensation on the KBr window.

2.2 Packing List

All PAC300 photoacoustic accessories include:

1. PAC300 with focusing mirror and KBr window.

2. Black handled sample holder (inserted in PAC300) with brass sample nest, five

small and five large removable sample cups, five nest spacers to elevate samples,

sample cup fixture and funnel, tweezers and Allen wrench to adjust cup o-ring

compression.

3. Carbon reference sample mounted in black handle.

4. Liquid crystal for imaging IR beam position.

5. Helium flow meter.

6. Hermetically sealed shipping/storage case

Some accessories may also include one or more of the following:

1. FTIR specific baseplate mounting.

2. Desk-top power supply.

3. Glassy carbon phase reference.

4. FTIR specific connection cable(s).

5. PAC300 elevation adjustment shims.

6. FTIR purge coupling.

7. SH003 and/or SH004 options.

2.3 Damage Inspection

Please examine items for evidence of shipping damage. Report any damage to the carrier

and to MTEC for direct purchases or the reseller that shipped the accessory.

3. PAC300 Description

3.1 Introduction to the PAC300

The PAC300

enables

direct

measurement by photoacoustic detection

optical

absorption spectra

lid

s and semisolids and is primarily used

FTIR

spectrometers:

http://www.mtecpas.com/Docs/Photoacoustic%20Technology%20Overview.p

df .

The

detector

can be

used

for

a wide

range

measurements

described

the

applications

liter

atur

e and literature bibliography:

http://www.mtecpas.com/applicationslibrary.html ,

http://www.mtecpas.com/Docs/FTIR%20PAS%20Bibliography%20Draft%205.pdf .

The PAC300 can also be used with nonvolatile liquid and noncorrosive gas samples which

are not toxic.

The PAC300 is

designed for

ease of use.

It mounts

in the

FTIR slide-

mount fixture or on FTIR specific baseplates. Sample changing, purging,

and

sealing

e controlled

by a

single lever, detector preamplifier

gain is

controlled

by a

position switch

on the

detector,

and

the detector

powered

either

by the FTIR or by a

115/230 V,

60/50 Hz desk top power

supply

with

an international standard IEC 320

input

connector. This

allows the power

supply to be

used with appropriate

cord sets for any country

of the world

Inserts into FTIR Slide Mount

Inserts into FTIR Sample compartment

PAC300 for slide mount fixture (left)

or baseplate mounting (right).

4. Set-Up Directions

4.1 Insert Rear Lever

The stainless steel rear lever is packed separately from the PAC300 in the shipping case

and should be inserted into one of the three slots on the back of the PAC300. Use the slot

that allows the lever to rotate most conveniently in your FTIR through the 90 degrees of

rotation necessary to purge and seal the sample. Note that the sample holder can be

inserted from either side of the PAC300 to accommodate both right-to-left and left-to-

right beam directions in different FTIRs.

Purge Inlet

Sample Holder

Rear Lever

FTIR Purge

Coupler

Baseplate

4.2 Mounting and Alignment of the PAC300 in the FTIR

The PAC300 is either mounted on an FTIR specific baseplate or in the standard sample

slide mount found in all FTIRs. Baseplate and slide mounted PAC300s are prealigned and

usually will not require the adjustments described below.

Alignment can be checked using the

nfrared heat

sensitive liquid crystals supplied

with the

PAC300.

Lever

Slots

Color Change Indicates

FTIR beam focal spot. If the

spot is centered in the cup,

the PAC300 is aligned.

PAC300 needs to be moved

horizontally perpendicular

to the IR beam to center the

spot in sample cup.

IR Beam

order

to check

alignment, place a liquid crystal in the sample cup following

these directions in its package:

Heat Sensitive Liquid Crystals (HSLCs)

The HSLCsare usedto alignthe photoacoustic detector in the FTIRby imaging the focal spot of the IR beam in the sample

cup. Each HSLC covers a slightly different ambient temperature range. The one best suited for a given ambient

temperature should be selected by trying each. Place a HSLC in the large sample cup supported on the foam spacer. A

brass spacer should be used under the foam to elevate the HSLC to a point near the cup rim. The heat sensitive side of

the HSCL can be identified by finger touch induced heating. The detector position should be adjusted to center the

focal spot image in the sample cup. See the Instruction Manual for additional information.

Then

block

the infrared beam

and

insert the sample holder with the

crystal

into the PAC300.

Fully

open the

aperture

of the

FTIR. Elevate

the

crystal

moving the rear lever

to the

CLOSED PURGE position. Remov

the

beam

block, wait

several seconds, remove

the

sample

cup, and

examine

the

image

pattern

before

it fades

the

temperature falls.

The

types

of images

that

may be

observed

are

shown

above. Image

indicates ideal alignment. Image

shows

ide

misalignment.

This can

corrected

moving

the PAC300

perpendicular

to the

beam

in the

direction opposite

to the

misal

gnment

direction. The side-to-side

adjustment

can be

made as shown below either

loosening

the

screws

on the

baseplate and

sliding the

PAC300

side-to-side

or by adjusting the

slide

plate

relative

its mounting

yoke.

Image

indicatesthat

the PAC300

needs

to be

raised. The height of

baseplate mounted PAC300s can be adjusted with the screws that support

the accessory on the baseplate as shown below.

PAC300 needs to be

moved vertically to

center the spot in sample

cup.

Shims for height adjustment

Side-to-side adjustment

In the case of slide mounted PAC300s, some

FTI

slide

fixtures have provision for

height adjustments

while

others

not.

is no

adjustment provided

on the

FTIR, height adjustments

are

made by placing, as shown above, small

shims provided with

the

detector between

the PAC300

lide

mount

and

the

yoke

coupling plate. Adding shims lowers the detector

and moves

e image

in the

direction

of the front of the PAC300

In some cases it may be desirable with slide mount fixtures to support the

PAC300 directly on the FTIR’s or other instrument’s baseplate. Four 5-40

thread screws can be used as adjustable legs as shown below.

If slide mount fixture’s position is designed to be adjustable in the direction of the IR beam

, it may be observed that the

infrared beam image on the liquid crystal

large

and

weak. This may be caused by

the PAC300 not being positioned properly relative

the IR beam’s focal spot which is normally at the midpoint of the beam’s path through the

FTIR's

mple compartment. The PAC300’s optics require that the PAC300’s

slide plate be coincident with the FTIR’s focal plane with the hole in its slide

plate centered on the focal spot of the FTIR. To achieve this, the slide mount’s

position can be adjusted while watching the PAC300’s interferogram signal to

maximize it.

This nut is one of four used to

raise or lower the PAC300 on

a baseplate mounted unit.

Four 5-40 Screws Support

the PAC300 and allow for

height adjustment.

FTIR’s focal spot

4.3 Electrical Connections

The PAC300 is powered either by the FTIR or an MTEC desktop power supply. The power

and signal cables are connected to the vibration isolated part of the accessory after first

being secured to the stationary part to avoid transmitting mechanical vibrations to the

PAC300’s sensitive microphone.

The desktop power supply has +15 and -15 Volt outputs and connects to either 115V 60 Hz

or 230V 50 Hz power lines. It has an IEC 320 power cord connector and an RJ9 output

connector.

The PAC300’s preamplifier gain is adjustable in 12 steps from 2X to 10,000X to

accommodate samples with different thermal properties and FTIR mirror velocities.

Power In

Signal Out

Gain Switch

On-Off switch

120/230 Volt

switch

4.4 Purge Gas Connections

Purging with Zero Grade Helium increases the signal by a factor of 2 to 3 and helps to exhaust

moisture and CO2 from the sample chamber. A two stage gas regulator valve should be

connected to a helium tank with its output connected to the MTEC flow meter. The

flowmeter output is connected to the inlet of the stationary part of the PAC300. Its outlet is

connected to the vibration isolated sample chamber. Consult Section 5.5 before purging the

PAC300.

5. Operation

5.1 Preamplifier Gain Control

twelve position switch controls

the gain as fo

llows

step# 1

5 6 7 8 9

gain

50 100 200 500 1000

2000

5000

10,000

factor

The gain

should

be set high

enough

to give an

inter

ogr

amplitude of

several volts

but not too high to

either cause preamplifier clipping

(<20V

to-peak)

or to

overloadthe FTIR's

A to D

converter.

Higher gains

are

used

for

higher

FTIR

mirror velocities because

the

signal

amplitude decreases

modulation frequency increases. Higher gai

are

also

used when sample spectra are

being

acquired relative

to c

bon

reference

background spectra because totally absorbing carbon

gener

tes

higher signal amplitudes than partially absorbing samples whichusually

have higher thermal mass.

To Gas

Cylinder

Line Pressure

Tank Pressure

Control Flow Rate

Only with this Valve

Leave This Valve

Always Open

Rear Lever Always In the SEAL

Position When Adjusting Valves

Flow Rate 10cc/s or Less

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